Introduction and application of twin screw extruder

Introduction and application of twin screw extruder

(1) Introduction of twin screw extruder

There are many types of twin-screw extruders, which can be divided into two categories: intermeshing and non-intermeshing. Intermeshing twin-screw extruders can be divided into two categories: co-rotating and counter-rotating.

The twin screw extruder contains the following multiple systems. The screw system mainly completes the plasticization and conveying process of the material, which has a great influence on the performance and quality of the finished product.

① Feeding system: including hopper, mixing motor, and feeding motor. It can prevent material accumulation and facilitate its smooth entry into the feed inlet.

② External heating system: mainly use heating rods and cylinders to efficiently heat up materials and promote plasticization.

③ Cooling system: Use a heat exchange system composed of heat transfer oil or water to reduce the heat of the fuselage, so as to effectively control the temperature of the cylinder.

④ Hydraulic screen changing system: Use replaceable filter screen to intercept impurities, improve the degree of plasticization, and ensure the uniformity and stability of the quality of the output materials.

⑤ Vacuum system: extract the moisture and other low molecular volatiles from the material.

⑥ Electronic control system: responsible for monitoring and controlling the related equipment of the main and auxiliary material system.

⑦ Screw system: The most important part of the extruder, which can be divided into conveying section, melting section (exhaust port), plasticizing section (vacuum port), and discharging section.

(2) Segmentation of twin screw extruder

The screw system of a parallel twin-screw extruder is generally divided into 4 sections: conveying section, melting section (exhaust port), plasticizing section (vacuum port), and discharging section.

① Conveying section: the function is to transport materials and prevent backfeeding.

② Melting section: In this section, the materials are fully melted and mixed through heat conduction and frictional shearing.

③ Plasticizing section: further melt and mix the ingredients of the material, with the function of distributing and dispersing mixing.

④ Discharge section: conveying and pressurizing, forming a certain pressure, making the materials more compact, and at the same time further mixing, to achieve the purpose of extrusion and granulation.

(3) Conveying elements

① Types are divided into: large lead and small lead.

② Lead use effect: the more the lead, the more the screw extrusion capacity, the shorter the material residence time, the weaker the material mixing ability.

③ The usual use method of small lead: The combination is gradually reduced, and it is used in the conveying section, melting section, and plasticizing section to increase the pressure and increase the melting; improve the homogenization of the mixture and the stability of the conveying volume.

(4) Shearing elements

① Direction classification: co-rotating and counter-rotating. Co-rotating, promote material flow and realize its function; counter-rotating, has the effect of refluxing the transportation of materials, prolongs the residence time of the materials, enhances the plasticizing capacity, and improves the mixing effect.

② Angle classification: generally 30 °, 45 °, 60 °, 90 °.

③ Function and effect: In the co-rotating, increase the staggered angle, reduce the conveying capacity, extend the residence time, and increase the degree of plasticization. For dispersion, the larger the angle, the more obvious the effect. Dispersion mixing is generally best at an angle of 45°, followed by 30°, and the worst is 60°.

④ The effect of the number of heads

In the positive direction(co-rotating), the fewer the number of heads, the greater the extrusion capacity, the greater the torque, and the better the mixing effect, but the less the shearing effect; In the reverse direction(counter-rotating), the smaller the number of heads, the smaller the extrusion conveying capacity and the better the mixing effect.